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Respiratory virus infections can have long-term effects on lung function that persist even after the acute responses have resolved. Numerous studies have linked severe early childhood infection with respiratory syncytial virus (RSV) to the development of wheezing and asthma, although the underlying mechanisms connecting these observations remain unclear. Here, we examine airway hyperresponsiveness (AHR) that develops in wild-type mice after recovery from symptomatic but sublethal infection with the natural rodent pathogen, pneumonia virus of mice (PVM). We found that BALB/c mice respond to a limited inoculum of PVM with significant but reversible weight loss accompanied by virus replication, acute inflammation, and neutrophil recruitment to the airways. At day 21 post-inoculation, virus was no longer detected in the airways and the acute inflammatory response had largely resolved. However, and in contrast to most earlier studies using the PVM infection model, all mice survived the initial infection and all went on to develop serum anti-PVM IgG antibodies. Furthermore, using both invasive plethysmography and precision-cut lung slices, we found that these mice exhibited significant airway hyperresponsiveness at day 21 post-inoculation that persisted through day 45. Taken together, our findings extend an important and versatile respiratory virus infection model that can now be used to explore the role of virions and virion clearance as well as virus-induced inflammatory mediators and their signaling pathways in the development and persistence of post-viral AHR and lung dysfunction.

Background: Interferon (IFN) inhibits viruses by inducing several hundred cellular genes, aptly named 'interferon (IFN)-stimulated genes' (ISGs). The only two RNA viruses of the Pneumovirus genus of the Paramyxoviridae family, namely Respiratory Syncytial Virus (RSV) and Pneumonia Virus of Mice (PVM), each encode two nonstructural (NS) proteins that share no sequence similarity but yet suppress IFN. Since suppression of IFN underlies the ability of these viruses to replicate in the host cells, the mechanism of such suppression has become an important area of research. This Short Report is an important extension of our previous efforts in defining this mechanism., Results: We show that, like their PVM counterparts, the RSV NS proteins also target multiple members of the ISG family. While significantly extending the substrate repertoire of the RSV NS proteins, these results, unexpectedly, also reveal that the target preferences of the NS proteins of the two viruses are entirely different. This is surprising since the two Pneumoviruses are phylogenetically close with similar genome organization and gene function, and the NS proteins of both also serve as suppressors of host IFN response., Conclusion: The finding that the NS proteins of the two highly similar viruses suppress entirely different members of the ISG family raises intriguing questions of pneumoviral NS evolution and mechanism of action.

Respiratory syncytial virus (RSV)-bronchiolitis is a major cause of infant morbidity and mortality and a risk factor for subsequent asthma. We showed previously that toll-like receptor (TLR)7 in plasmacytoid dendritic cells (pDCs) is critical for protection against bronchiolitis and asthma in mice infected with pneumonia virus of mice (PVM), the mouse homolog of RSV. This lack of redundancy was unexpected as interferon-β promotor stimulator-1 (IPS-1) signalling, downstream of RIG-I-like receptor (RLR) and not TLR7 activation, contributes to host defence in hRSV-inoculated adult mice. To further clarify the role of IPS-1 signalling, we inoculated IPS-1 -/- and WT mice with PVM in early-life, and again in later-life, to model the association between bronchiolitis and asthma. IPS-1 deficiency predisposed to severe PVM bronchiolitis, characterised by neutrophilic inflammation and necroptotic airway epithelial cell death, high mobility group box 1 (HMGB1) and IL-33 release, and downstream type-2 inflammation. Secondary infection induced an eosinophilic asthma-like pathophysiology in IPS-1 -/- but not WT mice. Mechanistically, we identified that IPS-1 is necessary for pDC recruitment, IFN-α production and viral control. Our findings suggest that TLR7 and RLR signalling work collaboratively to optimally control the host response to pneumovirus infection thereby protecting against viral bronchiolitis and subsequent asthma.

The pneumonia virus of mice (PVM) model is used to study respiratory syncytial virus (RSV) pathogenesis. The outcome of PVM infection varies in different inbred mouse strains, BALB/c being highly susceptible and C57BL/6 more resistant. As the disease symptoms induced by RSV infection can become more severe as people age, we examined the primary and secondary immune responses to infection with PVM in aged BALB/c and C57BL/6 mice. Based on clinical parameters, aged C57BL/6 mice displayed less severe disease than young adult mice when infected with 3000pfu of PVM-15, while BALB/c mice were equally susceptible at both ages showing significant weight loss and high levels of virus replication. Furthermore, after primary infection the CD4(+) T cell numbers in the lungs were higher in young adult mice, while the CD8(+) T cell numbers were comparable in both age groups and strains. When either C57BL/6 or BALB/c mice were infected with PVM as young adults and then re-infected as aged mice, they were protected from clinical disease, while virus replication was reduced. In contrast to mice with a primary PVM-infection, re-infected mice did not have infiltration of neutrophils or inflammatory mediators in the lung. BALB/c mice had higher virus neutralizing antibody levels in the serum and lung than C57BL/6 mice upon re-infection. Re-infection with PVM led to significant influx of effector CD4(+) T cells into the lungs when compared to aged mice with a primary infection, while this cell population was decreased in the lung draining lymph nodes in both mouse strains. After re-infection the effector CD8(+) T cell population was also decreased in the lung draining lymph nodes in both mouse strain when compared to aged mice after primary infection. However, the central memory CD4(+) and CD8(+) T cells were significantly enhanced in numbers in the lungs and draining lymph nodes of both mouse strains after re-infection, and these numbers were higher for C57BL/6 mice., (Copyright © 2015 Elsevier GmbH. All rights reserved.)